Sex. Murder. Mystery. Welcome to the party.

Harry Lockhart (Robert Downey Jr.) is basically a decent guy. Sure, he's a petty thief who skates through life on a shaky cocktail of dog-eared charm and cockeyed optimism, but he wants to do the right thing. He just doesn't know how, exactly.

Harry's perpetual bad luck takes a turn for the better when he and his partner are doing some after-hours Christmas "shopping" at a New York City toy store and the security alarm breaks up the party. In making his frantic getaway from the cops, Harry inadvertently stumbles into an audition for a Hollywood detective movie, and faster than you can say Jack Robinson, the producer flies him to Los Angeles for a screen test.

Thrust into the cutthroat world of L.A.'s pros, cons, losers and wannabes, Harry is teamed with tough-guy private eye Perry van Shrike (Val Kilmer), AKA "Gay Perry," to prepare him for his screen test. Gay Perry is ruthless, relentlessly tough and - you guessed it - gay. He also has little patience for Harry, who tries out his acting skills by passing himself off as a detective.

It seems like nothing short of destiny when the thief-trying- to-be-an-actor- impersonating-a-detective crosses paths with Harmony Faith Lane (Michelle Monaghan), an aspiring actress who needs his help. Inspired by her hero Jonny Gossamer, a fictitious hard-boiled private eye featured in a series of pulp detective novels, Harmony moved to Hollywood to pursue her dreams...but a few years and a lot of rejections later, she's facing the harsh reality that her best days may be behind her.

When the mysterious suicide of Harmony's sister intersects with a seemingly unrelated case that Harry and Gay Perry are investigating, they suddenly find themselves embroiled in a real-life murder mystery. Bodies surface and re-surface...long-buried family secrets erupt in present-day mayhem...and what began as a free trip to L.A. may result in Harry's one-way ticket to the city morgue.

If he's going to stay alive and become the hero that Harmony needs him to be, Harry will have to convince a reluctant Gay Perry to help him solve the case. He'll need to channel Jonny Gossamer's tough-as-nails swagger. And a little dose of luck - or is it fate? - wouldn't hurt, either.